1. Field of the Invention
The present invention relates to a device for receiving information travelling on two capacitively coupled information transmission lines, in particular for a motor vehicle.
2. Description of Related Art
Information receiving devices of this type are already known in the state of the art, and which are integrated into electronic modules used for example in information transmission networks of motor vehicles and comprising a comparator each input of which receives signals from an information transmission line and which is biased in such a way that in the absence of information on the line the device outputs a privileged item of information, referred to as recessive state.
In the state of the art each input of the comparator is connected to an information transmission line through a capacitor, as well as to a supply through a resistor and to earth through another resistor.
The resistors for biasing the inputs of this comparator are rated in such a way as to obtain different biasing voltages at the input terminals of this comparator whilst keeping a pairing-up of the resistors and of the capacitors such that a similar time constant is maintained on the two information transmission lines.
The advantage of this structure is the automatic return to the recessive state after a discharge of the capacitive networks, allowing the continuation of the transmissions by other modules connected to the network.
However, these devices possess a certain number of disadvantages insofar as the input voltage possesses a high threshold, whence arises a temporal distortion in the signals at the output of the comparator. This manifests, for example, by a modification of the cyclic ratio of the signals in the case of pulse-width modulation (PWM) encoding, which is prejudicial to good signal recognition and to good message synchronization.
Moreover, the time constants of the RC circuits formed at the terminals of this comparator are dependent on the transmission frequency and on the encoding of the bits.
Hence the aim of the invention is to resolve these problems by proposing an information receiving device which is simple and reliable and whose output signals are free of faults.